package ex15;

import java.io.IOException;
import java.io.InputStreamReader;
import java.io.BufferedReader;
import java.util.Locale;

public class Main {

	public static void main(String[] args) throws IOException {
		
		InputStreamReader it = new InputStreamReader(System.in);
		BufferedReader in = new BufferedReader(it);
		
		int[] p1 = new int[2];
		int[] p2 = new int[2];
		double distancia;
		
		String[] input = new String[2];
		String[][] inputLine = new String[2][2];
		
		for (int i = 0; i < input.length; i++) {
			input[i] = in.readLine();
			inputLine[i] = input[i].split(" ", 2);
		}
		
		p1[0] = Integer.parseInt(inputLine[0][0]);
		p1[1] = Integer.parseInt(inputLine[0][1]);
		p2[0] = Integer.parseInt(inputLine[1][0]);
		p2[1] = Integer.parseInt(inputLine[1][1]);
		
		distancia = Math.sqrt( Math.pow( p2[0] - p1[0], 2) + Math.pow(p2[1] - p1[1], 2) );
			
		System.out.format(Locale.ENGLISH, "%.4f\n", distancia);

	}

}